Re: [dhcwg] Query Regarding DHCP Lease time, Rebind Time and Renewal Time.

"David W. Hankins" <David_Hankins@isc.org> Mon, 01 November 2010 18:57 UTC

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Date: Mon, 01 Nov 2010 11:57:44 -0700
From: "David W. Hankins" <David_Hankins@isc.org>
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Subject: Re: [dhcwg] Query Regarding DHCP Lease time, Rebind Time and Renewal Time.
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On Sun, Oct 31, 2010 at 11:06:05PM -0500, Bernie Volz (volz) wrote:
>    If a client receives an IA_NA with T1 greater than T2, and both T1
>    and T2 are greater than 0, the client discards the IA_NA option and
>    processes the remainder of the message as though the server had not
>    included the invalid IA_NA option.
> 
> So, I guess the DHCPv4 client could considers the OFFER (or ACK)
> invalid. Another option would be to ignore the servers T1/T2 and just
> use the default values?

I think Ramesh is specifically asking about client-calculated T1/T2,
where the client has a clock granularity in seconds and is receiving
very low lease times.

Note that 3315 instructs the client to check for 'T1 greater than T2',
not 'greater than or equal.'  This made me wonder if T1 = T2 is legal
in DHCPv6, and implies as Ted suggests to schedule Rebind only.

I have wondered if this language was intentional or not; in other
places the document also uses the language that a client should select
(e.g. a retransmit timer) "between values x and y", and it seemed
strange to me that this wasn't made inclusive.


Anyway - I think in DHCPv6 there is a higher expectation that the
client implement timers in a higher resolution that whole seconds
(several references to centiseconds), but at the same time doesn't
seem to concretely specify that ability as a requirement.  So in
this case in DHCPv6 I would expect the Reply IA_NA/IAADR;

  T1 = T2 = 0
  preferred = valid = 1

To result in T1 = 1/2 second, T2 = 7/8ths, or similar defaults ("at
the client's discretion").

Although I can't imagine anyone doing that on purpose.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins